The invention relates to a circuit arrangement for a telephone station with earth connection to the central supply device for the purpose of post-dialing, where the telephone station is assigned a dialing and speech circuit, a polarity reversal protection device and a flash circuit.
The central exchange (telephone exchange) requires, for example, for post-dialing signals (consultation, etc.), a signaling mode which is in addition to the normal dialing information. It is dependent upon the central exchange whether signaling must take place by "flash" (loop interruption) or by grounding the ungrounded pole of the central supply device. Grounding or flash are triggered by the same key. A circuit arrangement has already been proposed in which the telephone station is automatically switched, depending upon the central exchange, to function for flash or signaling. If a signal is required, earth is connected to the earth terminal point of the telephone station. If no earth is connected, a flash function mode automatically exists. However, this circuit arrangement operates in the aforementioned manner when an earth signal is required only if the positive pole of the central supply device is earthed.